Acoustic delay device



Feb. 23, 1954 J. P. ECKERT, JR., ET AL 2,670,459

ACOUSTIC DELAY DEVICE original Filed oci. 31, 1947 5 sheets-sheet 1 JOHN u. MAUOHLY JOHN PRES/ER EOKERT JR.

Feb; 23, 1954 J. P. ECKERT, JR., l-:T AL 2,670,459

ACOUSTIC DELAY DEvIE 5 Sheets-Sheet 2 Original Filed 001.. 5l, 1947 l di u INVENTORS.'

JOHN W. MAUOHLY JOHN PRESPER ECKE/7T JR.

A TTOR/VE Y Feb. 23, 1954 J. P. Ecm-:R1 JR., ET AL 2,670,459

ACOUSTIC DELAY DEVICE Original Filed Oct. 31, 1947 5 Sheetys-Sheet 3 soo l INVENTORS.'

JOHN W. MAUGHLY l JOHN PRESPER EO/(ERT JR.

A TTORN Y Patented Feb. 23, 1954 ACOUSTIC DELAY DEVICE John Presper Eckert, Jr., Gladwyne, and John W.

Mauchly, Ambler, Pa., assignors to Eckert- Mauchly Computer Corporation,

Philadelphia,

Pa., a corporation of Pennsylvania Original application October 31, 1947, Serial No.

783,328. Divided and this application April 28,

1951, Serial No.

6 Claims. l

This invention relates to a memory device and various elements thereof, the memory device being of a type into which information may be introduced electrically and from which information may be secured electrically.

This application is a division of our application Serial Number 783,328 filed October 31st, 1947, now Patent No. 2,629,827, dated February 24, 1953.

Memory devices of the type just indicated are required in a large variety of means used for carrying out logical procedures wherein they have the function of receiving information, holding it and transmitting it when and if required.

wide variety of devices have been used for this f purpose. Mechanical memories as used in computing machines quite generally comprise series of Wheels, the angular positions of which determine the information which is stored. Electrical relays have also been used for this purpose,

information being coded to correspond to open or shut conditions of various contacts. Vacuum and gas tubes have also been used for this purpose, the information here also being coded in terms of conductive and nonconductive conditions of the tubes or in terms of ranges of potentials or the like.

`The various memory systems just described have deficiencies which become particularly evident when the storing of a large quantity of in- 1 formation is involved. All of these systems are mechanically complicated by reason of the multiplicity of their elements required when any large amount of information is to be stored. All

of them also involve the consumption of large amounts of power in their operation. Except for those systems involving vacuum tubes, they are also quite slow in operation when their speed is compared with that attainable by the use of vacuum tubes operating through the medium of electrical pulses.

One object of the present invention is the provision of a memory device operating on a principle quite different from any of the above. In accordance with the present system information is stored in a coded sequence of pulses, using that term in a quite broad sense, which pulses are caused to circulate through a path, after being introduced electrically into the input terminal of the path, travelling along the path for a particular delay or transit time and then being taken from the path electrically. What has been just referred to may be made clear by reference to several embodiments of the invention whichwill be described in detail hereafter.' In one preferred (Cl. S33-30) embodiment, for example, the electrical input pulses are caused to produce in a liquid or solid medium acoustic pulses which are propagated through the medium to a terminal thereof, the transit time being such that at any instant in the medium there will exist a train of pulses which, by their nature and sequence, are representative of stored information. At the end of the transmission path, the acoustic pulses are retranslated into electrical pulses. The output signals may be returned to the input to produce through the acoustic pulse transmitting medium a continuous recirculation of a pattern of acoustic pulses characteristic of the stored information.

Accordingly, one of the principal objects of the invention is to provide new and improved information storage means.

Another object of the invention is to provide new and improved signal delay apparatus.

Yet another object of the invention is to provide new and improved acoustic delay means.

A further object of the invention is to provide new and'improved impedance matched apparatus transforming electrical signals to acoustic signals and acoustic signals to electrical signals with minimum distortion or signal loss.

Still a furthear object of the invention is to provide new and improved apparatus for acoustically transmitting signals in a plurality of channels within the same medium with negligent cross-talk eiect.

Yet a further object of the invention is to provide new and improved acoustic delay apparatus having a plurality of signal output terminals along its delay path.

Another object of the invention is to provide a new and improved acoustic delay device having input and output terminals proximately positioned.

Still another object of the invention is to provide new and improved acoustic delay apparatus having a tank arranged to effect substantially twice the delay path ordinarily obtained for a given tank length.

Yet another object of the invention is to provide an acoustic delay means having an easily controllably stabilized delay interval.

The above objects as well as other objects of the invention will become apparent from the following description read in conjunction with the accompanying drawings in which:

Figure 1 is an axial section through a preferred form of mercury tank involved in the recirculation of acoustic pulses,

Figure 2 is a transverse radial section through suitably cut to produce shear waves to the substantial exclusion of longitudinal and transverse waves: for example, a BT-cut quartz crystal will produce almost pure shear Waves in a solid medium such as glass.

While mercury is the desirable liquid used for reasons hereafter discussed, other liquids may be used for the transmission of the acoustic Waves and in such cases the application of metal directly on the surface of the crystals by a plating process is desirable to provide proper conductivity to the crystal faces which may be in contact with an insulating liquid. However, owing to amalgamation of the ordinary plating metals with mercury, and since mercury is itself a conductor, it is desirable in the case of a mercury tank merely to provide a high polish on the crystal surfaces in contact with the mercury.

The result is essentially the same as that secured by additional plating.

While in cases where the standardizing of the form of the pulse delivered from the memory device is effected on each orbital transmission of a pulse or its equivalent, the strict preservation of an ideal wave curve form in the mercury element may not be essential for the functioning of the resultant pulse taken out of the register, for other reasons or at other times it is desirable to effect such preservation of pulse rise, top, and drop characteristics of the standard pulse in the Wave propagated in the mercury tank. For this purpose, a departure from conventional practice in the use of piezo-electric devices is made in this instance. As is known, under the influence of opposite potentials applied to plates at opposite sides of a piezo crystal oriented on a proper axis, the entire crystal becomes thickened or thinned, depending upon the polarity of the applied potential. This in our invention produces a movement of one face of the crystal against the mercury and the beginning of the propagation of a wave or pulse. Since the crystal has a finite thickness, the application of a potential in the form of a step function, in giving rise to a change of thickness at every point of the crystal, causes the production of an approximately linear rise of pressure in the mercury or other transmitting medium. The fall in the pressure following such rise is determined by both the characteristics of the crystal and of the tank. Some reflections from the crystal faces also appear. When, as here, pulses are to be transmitted at intervals of the order of one microsecond, more or less, these phenomena become material. They become manifest in lengthening of the pulse itself with interference or partial neutralizing of one pulse by another in transmission, by overlap and modification of rise time or of effective amplitude. When extremely closely spaced pulses are transmitted, it is necessary that they be of short length in relation to the time or space interval between discrete pulses in order that the potential of one may reach its zero value before another begins, and also in some cases so that intervening time may be available in which other devices may function in response to interspersed pulses of alternated timing. It is conceivable that a crystal might be of such thickness that response to a pulse having a duration of one quarter the period of pulse interval would produce a pulse or a length occupying all or more than the desired pulse interval. Consequently, in our invention, it is necessary that the thickness ofthe crystal be as nearlyas practicable proportionate to a desired minimum duration of the.

pulse, when this is short, or to the .interval between pulses, when this interval is short.

We have found that a quartz crystal response highly effective as compared Vto that of thicker crystals, may be obtained by reducing the thickness of the crystal to 0.015 inch with a good workable minimum of those effects which prevent sharp rises and falls of the transmitted pulses. across the crystal should be short relative to the wave period.

If connections are made across the face of the transmitting crystal 5t and an electrical source in a circuit giving rise to pulses, then on each pulse of the circuit, the crystal being nonconductive, a capacitive effect will be produced across the crystal accompanied by the expansion and contraction of the crystal as the potential rises or falls inthe circuit, the crystals being properly cut and oriented in relation to the polarities applied. The abrupt response of the crystals to such pulses will propage corresponding acoustic waves in the mercury in contact with one side of the crystal. By'means which will be explained hereafter, the crystal-actuating electrical pulses which we produce involve rise and fall characteristics such that a very abrupt rise and a very abrupt fall of potential or vice versa are produced within a very short time interval, say, one and one-hah` microseconds or less. There is ordinarily a tendency in the crystal duev to its natural resonant period to produce echo or secondary wave forms, but such function is undesired here, and due to the very closely similar acoustical impedance value of the crystal and the mercury or other medium in contact with the crystal, this tendency of the crystal is suppressed so that, except for minor and unimportant oscillations, acoustic waves limited essentially to a single planiform advancing front of compression, with a single planiform following rarefaction are produced. Such a wave then graphically represented would have a nearly vertical front or rise,

proportional to voltage applied, a flat top and a very sharp drop or fall at the back with no detrimental advance or following ripples, and an abscissa time value closely conforming to the duration of that electrical pulse across the crystal from which the acoustic Wave originates.

At the same time as a pulse is produced in the mercury there will also be produced a pulse or wave leaving the crystal in the `opposite direction and passing through the ceramic mounting. If this ceramic is chosen to have also substantially the acoustic impedance value of the crys-` ceramic backing to equal in kinetic energy valueA that propagated in the mercury. This wave propagated in the ceramic, though reflected from the bevelled end of the support and thereafter multiply reflected within the support, will not enter the mercury, the 1angles of reflection preventing this. After a number of such reflections, the energy of this wave is dissipated. Thus there are eliminated any reflecting, resonating, or other interfering distinguishable acoustic pulses that would impair the distinctness of any succeeding wave propagated from the crystal through the mercury by reason of an electrical impulse acting across the crystal and very closely following the rst transmitted pulse,

The Wave transmitted longitudinally through In general the transit time for a Wave` thalnercury`e acts: upon the receiver`` crystal 58': with piezeieffect, producing corresponding eleo. trical response inthe crystal. Between the faces, accordingly.,Y theredis manifested a difference of electrical potential whichv may1 be utilised for various.` purposes. as-` hereafter indicated; The

bevelled outer end-ofthe ceramic support for the receiving: crystal.I 58 reflects` pulsesA whichu it re ocio/es andi transmits themy `to the sideY of the ceramic supportv where such reflectionsaredis. sipatedfwithout .being fed back: into themercury.

Aside from providing good acousticimpedance match to minimizereections, theceramic supporthas-the.,functioniofimechanically supporting the fragile crystalto prevent accidentalV breakage;V

The above-mentionedPatentt No. 2,629,827 f disclosesarmaster oscillator and. temperature` con. trol'system. Thepurpose of this. system is. to provide i the pulses. for,l operation of the :complete systemwith automatica-control' to 1 avoid; troubles` due f to temperature changes. Mercury4 tanks of, thextype heretofore; described are such that vthe transmission times-of. pulses'. between the input and:` output arer quite. substantially.- affected by temperaturetothe` endtthat; ifa tank simultane-- ously. contains.V a quite large number.v of digital pulse spaces, relatively.fsmall'temperature changes may.; interfere-With tha emission .of-.one pulse at` the instantsome other pulse spaced. from the emitted" pulsef by; a predetermined. number isv enteringtthetank.A Itizmay be `here'noted thatltheacoustic velocity.- in'. mercury decreases withv rise ofavtemperature; Insurance .ofk proper. operation resultsfrom the use-.ot` the temperature control thewsametank withv the crystals e5 and 53"' :and .t

provides transmission ofpulees through thersame body -of mercury insures physical` similarity, with substantiallyl identicalz temperature variations; lcoyvever,` ifi-desired, two :separate tanksmaybe provided, individual .to rthe/tyco sets` of.. crystals, and so far as similar temperature variations are concerned'` these may 'be secured: byfhaving. the tanks insclose'. proximity to each other within, for-example; al common insulated'. enclosure.

It may be'u here again; remarked' that: the/tern:` perature-is desirabiy-:maintained .quiteiclosely conf-Y stantiand for thisfpurpose heat; maybe applied bycurrent through Athe heating coil 'i8 under 1con-` trol oiv athermostatresponsive to temperatures wit-hin Vthe; enclosure.1 Such thermostati'c; con-` trol', however, formsfno essential partici-the pres. ent 'invention and need not'V be describedv in. def taili 'Reterringlto Figure .3 there is illustrateditheref in a.mercury=tank having certain structural tfea.- tures which; .aswillbeevidentJy may be incorpo`m rated in. a: multipie Y tank'. of' the: typel peviousiyf detailedi IllietanicV comprises a metal tube i ASQ-.provided with aV filling opening A321 and with` interna-i shoulders 4342 and 4-3 B.- Washers 12382 of insulate. ingmaterial4 engage the shoulders 4314 andy 42:35; and inflatwiseengagement with them-are quartz crystals 44D ofVA the type previmisly described; Washers Mf-areprovded'f outside these crystals and; areengaged by theendsof insulating cups 4441which i are pressedl inwardly by the action on resilient washers-446 of screw caps-YMS-threaded on the endsfof the tube 436i. The internalkbot-etoms oi the cups 4-i facing the outer faces of the crystalsd are:provided withannularserration li which provide; facing the-crystals, anguelarly disposed Walls which, as Will be pointed out hereafter, tend to deectv disturbing reflec-` tions. Electrodes 452 having-inwardly directed; conical endsnand `threaded-stems passing through: the bottoms of thel cups 444 andare securedv thereto by nuts fi-5|. Connections 451i. andz451 are secured to these-terminal electrodes. A; con.-n nection '4511' serves to provide electrical conduca. tionfto vthetank 43d and the mercury. between' the crystals in the space 458.

The. space A58 between the crystal faces is.l filled with mercurylas are alsov the cavities 4&0- and 52 in the cuts 44. However, thesecavi. ties also preferably contain acoustcally absorbent material such as glass Wool or the likei for.- thev purpose of damping acoustic waves.propa. gated from theouter faces of the crystals.

As described previously in connection with-the crystals their faces. are desirably highly polished to secure good acoustic transmissionbetweenthe crystals and the mercury.

In the construction just described the portiony of the tube e36 between the shoulders 43B. and'.- fi constitutes ahollow tube-.containingmercury` continued by anend portionat each endof thisi tube carrying a piezo-electric crystal spacedbyi the Washers .$33 from the adjacent" end .offthetube. The cavities at 460. and vM52 providedl each of these endportionsopen towardtheoen. trai mercury tube and are closedby the faces, ofthe crystals. The opposite Wall of eachcavityby reason of the serrations at 45); is. angularly disposed with respect to the adjacent crystalL face and containsmercury. The'mercury in'each.` of these cavities is insulated from. themercury between the crystals-by the Washers-..4381 and442: pressed against the peripheries. of the crystals.. At eachend of theline an electrical connection. is .made through the electrode 50.tothe a mer. cury in thecavity and themercury in thehollow tube between the crystals is provided Withl an.- electrical' contact at 457'. As previously.: noted themercuryin the regions. 458, Aand 4623has= an acoustic impedance-substantially equal to the acoustic impedance of the-piezo-.electric crystals. The bodies of mercuryiurnish electrical contact; with the-crystal faces.

rEhe fact that there is animpedance match. between the crystals and the mercury. insures a minimum of reiiection ofacoustic waves: im pingingon a crystal so that thereceiving crystal", which may be-either of those indicated, is` sub stantially transparent to the acoustic Waves- Wnich pass therethrough tobepartially absorbed1v in the glass Wool or other iiller in the mercuryinthe end cavity while any. residual Waves reaching the ends of'the cavity are reflected at. such angles by the angularly disposed surfacesof the. serrations d50 that. they Willbeabsorbed, inthe. Walls of the cav-ities Without any substantia1- reiiection back tothecrystals; Accordingly, reections areminirniaed. Furthermore, byreason-Vl of the impedance match between the, crystals; and the mercury the crystals will notl continue to osciliate after thel first impingementi by; ai. pulse, but rather any. crystal oscillationsgwill beg quickly. damped. by: reason. ofi the; free; trauern-iS@-l sion of the energy to the mercury. The Q of the crystal is thus caused to be quite low.

While mercury is mentioned as the desired medium, it will be evident that liquids or substances other than mercury may be used .which have similar acoustic impedances. In such cases, however, if the liquid is a non-conductor, electrical connections must be made to the crystal faces through thin metallic coatings thereon.

While quartz crystals are highly satisfactory, it will be evident that they may be replaced by other crystals such as those of Rochelle salt which may loe-carried by glass plates for the purpose of providing necessary mechanical strength. In such cases, of course, metallic coatings are provided for the purpose of securing electrical conductivity to the crystal faces.

If individual mercury or othergtanks of the type just described or specically illustrated are used, instead of providing a pair of acoustic delay lines in a single medium, the two tubes thus substituted for the single tank should be closely contiguous to each other and within a common enclosure, preferably heat insulated, so that they partake of the same thermal variations. This will insure that they will not become so different in temperature, as to disturb the proper uniform continuous operation of the system.

In certain instances it is desirable to transmit to external systems or devices pulses in transit in a delay line from one or more intermediate locations between its ends. Figure el illustrates a type of acoustic delay line in which this is possible. A tank is formed of a series of sections 464, 456, and 468 (there being more or less than the three illustrated), which sections are bolted together at their contiguous ends. Input and output crystals at 41E) and 412 may be provided in any or" the fashions previously indicated. In this instance, however, there are provided at the joints between the various tank sections transparent piezo-electric crystal arrangements which, While permitting free transmission of pulses from the input crystal to the output crystal, will serve to permit the taking off of electrical pulses during the passage of acoustic pulses. For this purpose, crystals 414 and 476 are cemented to opposite surfaces of metal foil indicated at 418 or are cemented to each other, adjacent faces of the crystals being coated with metal to provide conductivity. The outer faces of the crystals are, of course, in conductive contact with the bodies of mercury in the several chambers. External connections from the metallic electrode between the crystals are taken oir as indicated at 4&2 and 484, the latter being from a crystal arrangement of 480 similar to that shown in section. For the purpose of preventing hydrostatic stresses the bodies of mercury in the various chambers are maintained Vin communication with each other through ducts 483 which communicate with chambers 485 formed in the flanges of the tank section.

rIhe crystals may be of quartz or of other Inaterial of piezo-electric character having' acoustic impedances as nearly as possible equal to that of mercury. Glass plates may be used for the mounting of ouartz or Rochelle salt crystals with suitable metallic coating provided to form the electrodes for the crystals. When the acoustic impedance is matched the crystals with or without backing form a substantially integral part of the mercurj7 body so that no material difference in transmission of acoustic pulses from the input to the output ends of the tank is perceptible as compared with a tank from which the intermediate take-01T devices are absent. As the pulses pass the intermediate piezo crystal or crystals, however, electrical signals will be given off which may be used externally. The purpose of taking off signals intermediate the ends of the delay line is that there may be,v in various instances, the desirability of securing a delay of take-off following the input to the line less than the transit time through the complete line. Sometimes it is desirable to take off simultaneously pulses in different memory spaces of the orbital circuit and this may be accomplished by the use of the tank just considered.

It may also be noted that, While pairs of crystals have been referred to at 414 and 4l6, one of them may be replaced by a support such as ceramic, glass or fused quartz which would be inactive from a piezo-electric standpoint. The support should, of course, be of a material forming a'proper impedance match with the liquid used to prevent reflections which might become confused with the transmitted signals.

Figure 5 illustrates still another form of tank in which reflection of pulses is provided so that for a given physical tank length there may be secured a pulse path equal to twice this length. Furthermore, pulses may be taken off at the point of reiiection. The tank in this case comprises a cylinder 486, the interior of which is filled with mercury or other liquid 488. A crystal 490 is cemented to a ceramic support 492 of the general type described in the rst tank modification but in this instance the crystal essentially functions as two separate crystals by being provided on its outer cemented face with separate metallic coatings continued as indicated at 494 and 496 for the making of external connections. Between these connections there is desirably provided an electrostatic shield in the form of a metallic plate 498 which-may be grounded and which is located between two separated portions of the support 492, these being cemented on opposite surfaces of the shield plate 498. At the opposite end of the tank a ceramic support 500 having the same acoustic impedance as mercury carries a crystal 502 coated on its surfaces with metal to provide electrical connections, the inner one of which may be grounded to the tank 485 while the outer one is connected through a wire 504 to a terminal mounted inthe lthreaded clamping member 506. In the operation of this tank, assuming that the upper portion of the crystal 490 is used for transmission and the lower portion for reception, eleotrical signals are applied through the conductive coating 494 and give rise to acoustic pulses by reason of the piezo-electric effect of the crystal. These are transmitted through the mercury column and through the acoustically transparent support 50c, being reflected by the cuter surface of the crystal, which, in this case, is backed up by Vair having an acoustic impedance quite different from that of the crystal. The reflected pulses are retransmitted through the support 5&6 and the mercury column to the lower portion of the crystal 49u, and through the piezo-electric effect, give rise to electrical signals which may be taken oi from the conductive coating 495. The transducers constituted by the upper and lower portions of the crystal 49u are essentially isolated from each other except for the reflection path just described. Direct waves from one portion to the other through the mercury are avoided due to the characteristic of a liquid as acoustic med ium for suppressing transverse modes of acoustic 11 waves. Selection of the proper vcrystal cut zaslsures vthat the `crystal will .be sensitive only for waves received along `paths:orthogonal to its face pla-ne.

Besides giving a halfway read-out point and 5 -cutting the length of the mercury column in half for a given delay Path this wtank has the advantage of keepinginput and output leads toassociated electronic equipment short, thus simplifying design.

.It will be obvious tcthose skilled in theart that the invention maynd wideapplication with appropriate modification to meet the individual design circumstances, but Without substantial departure from the essence of theinvention.

What is claimed is:

l. In an acoustic delay device; a plurality of transducers each comprising an acoustic signal attenua-tingsupport having Ya crystal mount- '.ing surface non-,parallel with its other bounding surfaces, a crystal having an exposed surface and an attaching surface, and an electrically conductive material between and adhering to said mounting surface of said support and the attaching surface of said crystal; a body having surface nonfparallel with its other bounding surfaces, a crystal having van exposed and an attaching surface, and an electrically conductive material between andradhering to said mounting surface of said support and the attaching surface Qsaid crystal; a cylindrical body having an enclosed. chamber and retaining said transducers arranged in pairs having their exposed crystal surfaces opposite and parallel to each other; and a iiuid within the chamber of said body and communicating with the exposed .crystal surfaces of said transducers.

3. -In an `acoustic delay device; a plurality of transducers each comprising an acoustic signal attenuating supporthaving a crystal mounting surface'non-parallel with its. other bounding surfaces, a crystal having ran exposed and an at- Erft taching suraca-and an electrically Aconductive material' between and adheringto saidzmounting surface of `said support and the attaching surface ci said crystal; a cylindrical body having an enclosed chamber and comprising two ends Walls substantially perpendicular to the cylindricalaxis retaining said transducers arranged in pairs havingtheir exposed crystal surfaces opposite and parallel to each other; and a iiuid within the chamber of said body and communicating with the'exposed crystalsurfaces of said transducers.

4, In anacoustic delay device; va plurality of transducers each comprising'an acoustic signal attenuating support having a crystal mounting surface non-parallel withits other bounding surfaces, a crystal having an exposed and an attaching surface, and an electrically conductive material between and adhering to said mounting surface of said support and the attaching surface `of said crystal; a cylindrical tank having an enclosed chainber'and comprising two end Walls substantialyperpendicular to the cylindrical axis retaining said transducers arranged in pairs having their exposed crystal surfaces opposite and parallel to each other; and mercury iiuid within the chamber of said tank and communicating with the exposed crystal surfaces of said transducers.

5. The combination according to claim 1 in which one transducer ofveach pair is an input transducer for transforming electrical signals into acoustic signals for propagation through said liquid, and the other transducer of each pair is-an output transducer for transforming. into electrical signals the acoustic signals propagated from its corresponding input transducer.

6. The combination according to claim 5 in which the input and output transducers of each pair have substantially the same acoustic path spacing to provide substantially the same transit time for each pair.

JOHN PRESPER ECKERT, Jui J Ol-IN W. MAUCHLY.

References Cited in the le of this patent UNTIED STATES PATENTS Number Name Date 2,421,026 Hall et al. May 27, 194'? 2,423,306 Forbes et al. July l, 1947 2,431,862 Carlin Dec. 2, 1947 2,540,720 Forbes et al. Feb. 6, 1951 

